Wide ranges of medical treatments have been developed using endoluminal prostheses, which are medical devices adapted for temporary or permanent implantation within a body lumen, such as naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include arteries such as those located within coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed with particular structures to modify the mechanics of the targeted luminal wall.
A number of vascular devices have been developed for replacing, supplementing, or excluding portions of blood vessels. These vascular devices include endoluminal vascular prostheses and stent grafts. Aneurysm exclusion devices, such as abdominal aortic aneurysm (AAA) devices, are used to exclude vascular aneurysms and provide a prosthetic lumen for the flow of blood. Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually from disease or a genetic predisposition, which can weaken the arterial wall and allow it to expand. Aneurysms can occur in any blood vessel, but most occur in the aorta and peripheral arteries, with the majority of aneurysms occurring in the abdominal aorta. An abdominal aortic aneurysm typically begins below the renal arteries and extends into one or both of the iliac arteries.
Aneurysms, especially abdominal aortic aneurysms, are commonly treated in open surgery procedures in which the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While open surgery is an effective surgical technique in light of the risk of a fatal abdominal aortic aneurysm rupture, the open surgical technique suffers from a number of disadvantages. The surgical procedure is complex, requires a long hospital stay, requires a long recovery time, and has a high mortality rate. Less invasive devices and techniques have been developed to avoid these disadvantages. Tubular endoluminal prostheses that provide a lumen or lumens for blood flow while excluding blood flow to the aneurysm site are introduced into the blood vessel using a catheter in a less or minimally invasive technique. The tubular endoluminal prosthesis is introduced in a small diameter crimped condition and expanded at the aneurysm. Although often referred to as stent grafts, these tubular endoluminal prostheses differ from covered stents in that they are not used to mechanically prop open natural blood vessels. Rather, they are used to secure an artificial lumen in a sealing engagement with the vessel wall without further opening the abnormally dilated natural blood vessel.
Stent grafts typically include a support structure supporting a graft material, such as woven polymer materials, e.g., Dacron, or polytetrafluoroethylene (PTFE). The graft material is secured to the inner or outer diameter of the support structure, which supports the graft material and/or holds it in place against a luminal wall. The stent graft is secured to a vessel wall above and below the aneurysm. A suprarenal spring stent of the stent graft can be located above the aneurysm to provide a radial force which engages the lumen wall and seals the stent graft at the lumen wall. The suprarenal spring stent extends beyond the graft material, so that blood can flow to renal arteries located at the suprarenal spring stent. The suprarenal spring stent can include hooks to puncture the vessel wall and further secure the stent graft in place.
One shortcoming in present stent graft designs is the adequacy of sealing at the proximal end. Flow channels can form between the graft material and the lumen wall where the suprarenal spring stent is not holding the graft material in contact with the lumen wall. Blood flow enters the flow channel, rather than the stent graft lumen, thus continuing to stress the wall of the aneurysmal sac.
Another shortcoming in present stent graft designs is the inability to accommodate individual abdominal aortic aneurysm geometries, such as a short AAA neck, tortuosity in the AAA, or an angulated AAA. A short AAA neck can preclude use of a stent graft, because there is not room to seal the stent graft at the lumen wall. Tortuosity or angulation can prevent an adequate seal, make placement of an inflexible stents graft more difficult, and increase stress on the stent graft.
Yet another shortcoming in present stent graft designs is ease of deployment. The body spring stents are placed close together to keep the graft material between the body spring stents out of the stent graft lumen when the stent graft is deployed, but placing the body spring stents close together reduces the stent graft flexibility and make the stent graft more difficult to maneuver through the tortuous path to the AAA. In addition, the body spring stents are usually rings with a regular sinusoidal pattern, so that the apices of the rings line up when the body spring stents are crimped. This increases the bulk of the material at the level of the apexes and thereby the diameter of the crimped stent graft and makes it harder to maneuver into place.
Yet another shortcoming in present stent graft designs is ease of manufacture. Bifurcated stent grafts include an ipsilateral limb and a contralateral limb for deployment in the iliac arteries. The diameter of the ipsilateral limb is typically larger than the contralateral limb, so different limb spring stents are used, complicating manufacture. The contralateral limb spring stent must cleanly open the contralateral limb during deployment so that a guide wire can be advanced through the contralateral limb.
It would be desirable to have an endoluminal prosthesis that would overcome the above disadvantages.